class Solution {
    public int tribonacci(int n) {
        int[] dp = new int[39];
        dp[0] = 0;
        dp[1] = 1;
        dp[2] = 1;
        if (n >= 3) {
            for (int i = 3; i <= n; i++) {
                dp[i] = dp[i - 1] + dp[i - 2] + dp[i - 3];
            }
        }
        return dp[n];
    }
}